[Gasification] making wood pellets

[list at sylva.icuklive.co.uk]

On Tue, 5 Sep 2006 05:30:10 -0700 (PDT), Toby Seiler wrote:

>  Do you think there a threshold level like 1-5% that would make a difference in making pellets?  I have seen a website using up to 20% and the heat goes up a lot (btu per pound to 12k or so). 

I've lots of theories but no practical knowledge, I do have access to
a secondhand low pressure ring die but not the wherewithal to get it
going at the moment. There are lower limits for "contraries" in
pellets but I think that's more to do with the practicalities of
keeping the rawstock pure. I know the testing was quite sensitive
because it flagged up a problem with the lithium based grease being
used in the bearings getting into the pellet.

We have to be clear that the plastic proposed to serve the purpose of
lubricating (hence less die wear) and bonding the pellet (enabling
less pressure and power), not to facilitate the burning of plastic.

> Is the practice banned due to emissions or because most 
>commercial stoves can't handle the additional heat input?  

Almost certainly to do with emissions and perceptions of what is
allowable in the waste regulations. In UK these have become quite
stringent, even allegedly forcing one charity to cease collecting
unused, un opened, medicines for distribution in the third world.

At the same time there have been a number of corrosion issues
associated with PVC contaminated pellets (I do not advocate using
other than uncontaminated packaging plastic).
>   
>  As far as adding heat, my thought was that the pellet mill could
> have a preheater in front of it for the unconsolidated material. 
> Then upon entering compression in the mill the heat would be internal,
> not derived from the ring.  One could target just under pyrolysis temp 
> exiting the pelletizer.

I think you miss the point of my post, there is sufficient heat in the
die to do this in any case. The preheating would only be necessary in
a slower or lower pressure pelleting system. I do believe there is
scope for a novel lower pressure system for making pellets.

AJH